Telephone circuits



Jan. 11,1927. 1,614,443

w. T. POWELL I TELEPHONE CIRCUITS Filed A rii 5, 1924 INVENTOR Wmfrad T Powell ATTO EY Patented Jan. 11, 1927.

A UNITED STATES WINFRED T. POWELL, OF ROCHESTER, NEW YORK, ASSIGNOR TO THE STROMBERG' PATENT OFFICE.

CARLSON TELEPHONE MANUFACTURING COMPANY, OF ROCHESTER, NEW YORK, A

CORPORATION OF NEW YORK.

TELEPHONE CIRCUITS.

Application filed April 3, 1924.

This invention relates to telephone circuits and more particularly to the circuits of a telephone set including a receiver and a transmitter.

It is an object of the present invention to provide circuit arrangements which will deliver the maximum amount of energy in the form of an outgoing signal to a telephone line and which will receive the maximum amount of energy in the form of an incom ing signal from said telephone line without the disturbance of the receiving circuit by the transmission circuit, which disturbance is commonly known as side-tone in the receiver. In other words it is the object or the invention to provide a circuit arrangement for preventing talking currents from the talking net-work from interfering seriously with the receiving net-work.

In the embodiment of the invention herein described well-known substation equipment such as a receiver and a signal or ringer, are associated in a circuit net-work with a two-element transmitter and an induction coil having a secondary winding which is tapped at an intermediate point.

In the drawings Fig. 1 diagrammatically represents the invention applied to the substation circuits of a manual telephone line. Fig. 2 shows a similar substation circuit arrangement in which an impulse transmitter with a make-break type of shunt spring combination is provided. Fig. 3 shows a substation circuit arrangement provided with an impulse sender similar to that shown in Fig. 2, except that the shunt spring combination includesthree normally open contact springs.

The transmitter herein referred to as a differential microphone, may consist of a diaphragm, on each side of which a carbon button impinges. Other types of transmitters such as electromagnetic or electrostatic transmitters may be employed.

The impulse transmitter or sender herein referred to, may be similar in construction to that disclosed on pages 34 and 35 of Automatic Telephony, by Smith and Campbell, first edition but in which the shunt spring combinations are differently arranged.

Referring to Fig. 1, 5 designates the well known type of receiver associated with a differential microphone, which consists ot a diaphragm 6 on either side of which carbon Serial No. 703,895.

buttons 7 and 11 impinge. The primary winding of an induction coil is. indicated at 8, while the secondary winding of this induction coil is tapped at its mid-point to form windings 9 and 10 which are oppositely wound. It will be seen that the ringer 13 is bridged across the line conductors 14 and 15 in series with the condenser 12. The receiver 5 when removed from the switchhook closes contacts 32 and 33 in the well known manner and thereby completes a circuit for the receiver 5 by which incoming currents pass over the line conductor 15, primary winding 8 of the induction coil, hookswitch contacts 32 and 33, receiver 5 through the condenser 12 and thence to the line conductor 14. The two electrodes 7 and 11 of the transmitter with the secondary windings 9 and 10, of the induction coil are included in shunt of the circuit including the receiver 5 and the condenser 12. This shunt can be so designed that it offers high impedance to the incoming signals, thereby forcing them through the receiver 5, which with the condenser 12 in the series circuit can be so proportioned as to offer low impedance to the mentioned incomingsignals.

When this net-work is used to transmit outgoing currents, such currents do not produce serious side-tone noises in the receiver 5. Let it be assumed that at some instant the button 7 is being compressed and the button 11 is being expanded. The resistance of the button 7 is therefore decreased, while the resistance of the button 11 is increasing to cause an increasing flow of current through the secondary winding 9 and a re duced How of current through the secondary winding 10. If the current over the conductors 14 and 15 is in the direction shown by the full line arrow and if an increase of current throughthe winding 9 induces current in primary winding 8 in the direction shown by the dotted arrow, the decrease in current flowing through secondary winding 10, at this time causes a further increased flow of current through the primary winding 8 as shown by the heavy dotted arrow. This is due to the fact that the secondary windings 9 and 10 are oppositely wound.

If at a certain other instant, button 11 is being compressed and button 7 is being expanded, the effect is opposite to that described under the previous condition, since in. oppositionrto the linecurrent. to reduce the current .fiow. overrthe; telephone line. Since these increases and decreases of current flow pass through the transmitter buttons 7 and 11 instead of being-impressed across the receiver, the side-tone action through the receiver 5 isreduced.

Referringto Figx Q thenetqvork of Fig. 1 has been modified "to incorporate awell known type.ofiimpulse sender, also known as a dial,'which is equipped withithe make-break type of shunt spring combina-. tion. The transn'iitti-ng;circuit of Fig, .2 diflers from that .describedin Fig; 1 by the inclusion of the impulseisprings 16,1 but-the circuit of :the receiver 5 during the recep tionof signals is. theisame as the net-work olxl ig. 1.. The. normally closed contacts 17 ot' the slnintuspringcombination, however, are opened-by the-operationof the impulse sender,. in order that disagreeable clicks may not be heard inVt-hereceiver ,Sduring the transmission: of. impulse The normally openedscontacts. 18 are closed during the operation. ofthe impulse. sender so that duringsthe sending ot impulses the impedanceot-the -diiferential microphone. is. not included in the signaling circuit extending through the .line conductors let and 15.

Ill rt-lle modifiednform of theinvention shown iii-Fig. 3,-the circuit arrangement difi'ers from Fig; 1- by-greason-ofthe fact that air impulse-sender provided-.with ashunt spring combination .having three normally open contacts, -is.- used and a different. hookswitch spring ,combinationiis employed In this arrangement it will be .notedthat the receiver 5, as awellias the differential microphone are-shunted when .thendial is operated to closeatheshunt sp.rings19, 20 and 21.. I11 thisiinstancealso the impulse springs .16 are serially included inzthe telephone line represent'ed'by the. conductors 14 and 15.

hat I 'iclaim is:

1. In a telephone net-work, apair 01. line conductors, a bridgeacrosssaid conductors, a diilierentialrmicnophone having its elements connected in a multiple in 1 said 1 bridge, a receiver connected i inshunt of :a portion of said bridge, and an impulse-isender having impulse springs :in '.said\ bridge: and oilnormal springs for controlling said receiver connection.

23 111 a telephone net-Work; a pair of line conductors, a bridge acro'ss said conductors, atransmitter comprising a diaphragm and a button engaging eaclrlside of ssaid diaphragm, the b1'1t-tons-of said transmitter being connected in multiple in said bridge a receiver connected in shunt ota portion of said bric g -,-and an inrpulse-asender having impulse springs in said bridge and offnormal springs for controlling said receiver connection.

3. In a telephone net-work, a pair of line conductors, a bridge acrossasaid conductors,

av differential microphone having itselements connected in multiple in said bridge, a cir cuit in shunt ot a portion of said bridge, a receiver and condenser in series in said shunt circuit, and a circuit normally closed across said conductors including a ringer and said condenser in series.

l. in a telephone network, a pair of line conductors, a bridge across said conductors, a differential microphone telephonically connected in said bridge, areceiver 'and'a'ringer telephonizally related to said line conductors and said bridgeby conductors, and 'a condenser common to said conductors.

5. In a telephone net-work, a pair of line conductors, a bridge across said conductors,

a differential microphone havingits elements connected in multiple in'said bridge, a circuit in shunt of said bridge, a receiver'in said shunt circuit, a hookswitch"for normally-opening said bridge and said shunt circuit, and an impulse sender having impulse springs in said bridge and other springs to complete a lay-path about said transmitter during the operation of said impulse sender.

6. .In a telephone net-work, a pair of line conductors, a bridge across said conductors, a differential microphone having its elements connectedin multiple in said bridge, a..cir cuit in shunt of said bridge, a receiver in said shunt circuit, a hookswitch for. normally opening said bridge and said shunt circuit, a ringer normally connected in a conductor across said line conductors, and a condenser common to said shunt circuit and to i said ringer conductor.

7. Ina telephone. net-Work, a pair of line conductors, a bridge. including a dilierential microphone connected across said line con ductors, asecond bridge includinga ringer and a condenser connected across said line conductors, and a third'bridge including a receiver connected to points on said first two bridges.

8.. In a telephone. network, a pair of line conductors,'a bridge including a dili'erential microphone connected across said line conductors, asecond bridge inclndingaringer and a condenser connected across saidline conductors, and a thirdhbridge including a series with two portionsinmultiple of the secondary windingofsaid induction coil, a transmitter having an element 1n series with ill llh)

Ill)

each portion of said secondary winding, and a receiver and a ringer electrically associated with said bridge and line conductors.

10. In a telephone net-work, a pair of line conductors, a transmitter comprising a diaphragm and a transmitter button engaging each side of said diaphragm, an induction coil including a primary coil and a secondary coil, said secondary coil having two portions which are substantially equal, oppositely wound and connected with respect to each other, a bridge across said line conductors, said bridge including said transmitter buttons and the portions of said secondary coil in multiple but in series with said diaphragm and said primary coil, and a receiver associated with said line conductors. 11. In a telephone net-Work, a pair of line conductors, a three-electrode transmitter, an induction coil including a primary winding and a secondary winding, said secondary winding having two portions which are substantially equal, oppositely wound and connected with respect to each other, a; bridge across said line conductors, said bridge including certain of said transmitter electrodes and the portions of said secondary winding in multiple but in series with said primary winding, and a receiver associated with said line conductors.

12. The method of reducing side-tone in a telephone substation circuit which comprises generating by means of a differential microphone, currents through substantially equal and oppositely wound secondary windings of an induction coil, the primary of which is included in the receiver and line circuits in series. I

13. The method of reducing side-tone in a telephone substation circuit which comprises generating currents through substantially equal and oppositely wound secondary windings of an induction coil, the primary of which is included in the receiver and line circuits in series.

14. lhe method ofreducing side-tone in a telephone substation circuit which comprises generating by means of a differential microphone, currents through two substantially equal and oppositely Wound windings of an induction coil, a third winding of said induction coil being included in the receiver and line circuits in series.

In witness whereof, I hereunto subscribe my name this 1st day of April, A. D. 1924.

VVINFRED T. POWELL. 

